//Definition for a binary tree node.
class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

public class Solution {
    public int sumOfLeftLeaves(TreeNode root) {
        if(root == null) return 0;
        if(root.left != null && root.left.left == null && root.left.right == null) {
            return root.left.val + sumOfLeftLeaves(root.right);
        }
        return sumOfLeftLeaves(root.left) + sumOfLeftLeaves(root.right);
    }
}